The impact of alternative mission models on the future orbital debris environment

In reviewing discussions of future directions for space activity, it becomes obvious that there are a large number of groups formulating a wide diversity of plans for the future use of space. These plan alternatives are being made to account for user needs, technology development constraints, economic constraints, and launch support, and each of the plans will have direct or indirect effects on the orbital debris environment in terms of mass to orbit, deposition of operational debris, and control of accidental breakups. Thus it is important to develop the ability to project future debris states for a range of possible space traffic scenarios. The impact that these possible traffic environments would have on space operations forms the basis for studies of alternative options for the usage of space. In this paper, the effects on the orbital debris environment of a base-line mission model and two alternatives are investigated, using a numerical debris environment simulation code under development at JSC.     

Productivity and food value of Amaranthus cruentus under non-lethal salt stress.

Stress effects from the accumulation of metal salts may pose a problem for plants in closed biological systems such as spacecraft. This work examined the effects of salinity on growth, photosynthesis and carbon allocation in the crop plant, Amaranthus. Plants were germinated and grown in modified Hoagland's solution with NaCl concentrations of 0 to 1.0%. Plants received salt treatments at various times in development to assess effects on particular life history phases. For Amaranthus cruentus, germination, vegetative growth, flowering, seed development and yield were normal at salinities from 0 to 0.2%. Inhibition of these phases increased from 0.2 to 0.4% salinity and was total above 0.5%. 1.0% salinity was lethal to all developmental phases. Onset of growth phases were not affected by salinity. Plants could not be adapted by gradually increasing salinity over days or weeks. Water uptake increased, while photosynthetic CO2 uptake decreased with increasing salinity on a dry weight basis during vegetative growth. Respiration was not affected by salinity. After flowering, respiration and photosynthesis decreased markedly, such that 1.0% NaCl inhibited photosynthesis completely. Protein levels were unchanged with increasing salinity. Leaf starch levels were lower at salinities of 0.5% and above, while stem starch levels were not affected by these salinities. The evidence supports salt inhibition arising from changes in primary biochemical processes rather than from effects on water relations. While not addressing the toxic effects of specific ions, it suggests that moderate salinity per se need not be a problem in space systems.     

User issues and Earth observation data policy

The second workshop of the EOPOLE project was held in Cosenza, Italy, 10–12 May 1999, organised by Microwave Consultant Engineering (MiCE). Its purpose was to address the user issues related to Earth observation data policy. This report presents the main conclusions of the workshop. The different approaches among lead departments within national governments emerged as one of the main areas of which users in Europe need to be aware.     

Need and effect of reconditioning of nickel/hydrogen batteries

There has been a debate about the need for reconditioning nickel/hydrogen batteries in geosynchronous satellites. A study was done as part of life cycling, to determine the necessity of reconditioning and its effect on the cell performance. A 36 Ah nickel/hydrogen cell was put on a GEO simulated cycling at 15°C without reconditioning up to four eclipse seasons. The effect of reconditioning on the fifth and sixth eclipse seasons was studied. The study has conclusively proven the need for reconditioning and has shown the benefits of a high rate reconditioning. It has also been possible to draw some conclusions about the effect of a long duration trickle charge on the positive electrode     

Raindrops on Titan.

Some of the aspects of methane precipitation on Titan are considered. In particular, descent velocities are computed. It is found that raindrops fall much slower than on Earth. Additionally, the maximum size of raindrops on Titan is over 9 mm, compared with under 6 mm on Earth. The composition of drops will vary with altitude. Implications of these properties for Titan and the Huygens mission are considered.     

Using open networking standards over MIL-STD-1553 networks

Over the past several decades, the MIL-STD-1553 networking technology has found use in a number of military and aerospace platforms, including applications on aircraft, ships, tanks, missiles, satellites, and even the International Space Station. In developing software applications for these platforms, the use of modern, open networking standards such as TCP/IP is often preferable. The Internet Protocol (IP) provides communications routing, and the Transmission Control Protocol (TCP) provides reliable delivery to the application level. Furthermore, higher-level protocols such as the HyperText Transfer Protocol (HTTP), the File Transfer Protocol (FTP), etc. can be utilized in a TCP/IP environment. Though these open communications standards are preferable for many situations, the MIL-STD-1553B standard does not immediately lend itself to TCP/IP communications. One of the reasons for this is the fundamental difference between the MIL-STD-1553B networking standard, which relies on a bus controller to control communications and other data link layer networking protocols such as IEEE 8023 (Ethernet) which are Carrier Sense Multiple Access (CSMA) networks, and are thus decentralized. Despite differences in MIL-STD-1553B networking and more traditional data link layer networking protocols, there is nothing fundamentally preventing IP communication over a 1553 network. We have implemented a method of encapsulating IP datagrams within MDL-STD-1553B data messages that allows for transparent use of Internet Protocol (IP) APIs at the application level. Our system allows traditional 1553 messages to also be transported over the network, and even allows traditional messages to take a higher transmission priority over IP traffic. We analyze the advantages of such a system and the performance level we achieved with our implementation of this concept.     

Aviation data networks: security issues and network architecture

The information technology (IT) revolution, combined with people's need to access information quickly, has resulted in the explosive growth of the Internet in the past decade. Ubiquitous access to the Internet has become an essential component of a mobile workforce, and multiple mechanisms are being devised to ensure seamless connectivity to corporate resources. An integrated security framework requires careful consideration of the security features of the network within an airplane. Potentially, the aircraft could consist of three kinds of networks, namely: passenger network, crew network, and control network. The security protocol implemented must ensure a proper separation of these networks and also watch for any security protocol violations. In this paper, the authors review existing aircraft data network standards, security provisioning, and security threats associated with the aircraft data networks. In addition, the authors also analyze the security threats associated with different network architectures.     

Ultra triple-junction high-efficiency solar cells

Solar cells suitable for the space environment must combine high-efficiency, high energy density, and radiation hardness in a manufacturable design. As improvement in one performance parameter usually results in degradation in one or more of the remaining parameters, careful optimization is required to enhance overall performance. The ultra triple-junction cell developed builds upon the established success of the fully qualified improved triple-junction cell currently in production. In the ultra triple-junction cell configuration, improved robustness and efficiency after radiation exposure augment a cell design expected to deliver 28% beginning-of-life efficiency in production.     

Overview of TeV gamma ray observations

TeV emission has been observed with high signal-to-noise from: two pulsar-driven supernova remnants, the Crab Nebula and PSR B1706-44 and a blazar class AGN, Markarian 421. Other sources, observed without the benefit of major background reduction techniques, are some of the compact object binaries. These discoveries plus the discoveries of EGRET of more than 130 sources at lower energies point to a growing number of scientific questions capable of being addressed by this field (particularly for distant sources via intergalactic absorption processes). Rapid further development will come as new instruments employing a variety of background reduction techniques come on-line.